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DNA STRUCTURE & REPLICATION
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DNA Structure & Replication - Jaguar Biologyjaguarbiology.weebly.com/uploads/5/9/8/6/59865823/... · DNA REPLICATION •DNA Replication is the copying process by which a cell duplicates

Jun 17, 2020

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Page 1: DNA Structure & Replication - Jaguar Biologyjaguarbiology.weebly.com/uploads/5/9/8/6/59865823/... · DNA REPLICATION •DNA Replication is the copying process by which a cell duplicates

DNA STRUCTURE & REPLICATION

Page 2: DNA Structure & Replication - Jaguar Biologyjaguarbiology.weebly.com/uploads/5/9/8/6/59865823/... · DNA REPLICATION •DNA Replication is the copying process by which a cell duplicates

A MODEL OF DNA

• In 1953, two scientists named Watson & Crick

built a model of DNA that demonstrates its

exact structure and function.

• They called this model a double helix, which

is also often referred to as a twisted ladder.

• A woman named Rosalind Franklin is actually

responsible for performing an x-ray on a

chromosome. This initiated Watson & Crick’s

double-helix design.

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DNA: THE THREAD OF LIFE

• DNA (also known as deoxyribonucleic acid) is a long molecule that makes up our chromosomes & is located inside the nucleus of a cell.

• DNA is known as the thread of life because it contains all of the information to direct our body’s functions in order to sustain life.

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CHROMOSOMES

• Chromosomes are made of

DNA

• Segments of DNA in specific

patterns are called genes

• Chromosomes are not always

visible. They are uncoiled and

as loose strands called

chromatin

• When it’s time for the cell to reproduce,

they condense and wrap up very tightly

to form a chromosome

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THE ROLE OF DNA

• The DNA that makes up genes must be capable of storing,

copying, and transmitting the genetic information in a cell.

• The 3 functions of DNA are:

• 1. Storing Information

• 2. Copying information

• Before a cell divides, it must make a complex copy

of every one of its genes

• 3. Transmitting information

• DNA must be carefully sorted and passed along

during cell division so that it is transmitted from one

generation to the next.

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THE STRUCTURE OF DNA

• DNA is a long molecule made

up of monomers called

nucleotides

• Nucleotides are made of three

parts

1.5-carbon sugar

(deoxyribose)

2.Phosphate group

3.Nitrogenous base

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NITROGENOUS BASES

• There are four kinds of nitrogenous bases.

• They are divided into two types- purines and pyrimidines.

• Purines: Adenine and

Guanine

• Pyrimidines: Cytosine

and Thymine

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BASE PAIRING

• Because of the size and shape of the

nitrogen bases, there are certain ones

that always pair together.

• Adenine & Thymine (A-T)

• Cytosine & Guanine (C-G)

• Chargaff’s Rule states that the pyrimidine

& purine bases have a 1:1 ratio

• The amount of guanine is equal to cytosine

• The amount of adenine is equal to thymine

• These nitrogenous bases form the

rungs/steps of the DNA molecule

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HYDROGEN BONDS

•Weak hydrogen bonds form between the nitrogen

bases to hold the two strands of DNA together

• Adenine and Thymine are held together by a double hydrogen bond

• Cytosine and Guanine are held together by a triple hydrogen bond

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DNA’S ANTIPARALLEL STRUCTURE

• The strands of DNA are

antiparallel

• the two strands run in

opposite directions

• All DNA strands are

read from the 5' to the

3' end

• the 5' end ends with a

phosphate group

• the 3' end ends with a

sugar molecule

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DNA REPLICATION

• DNA Replication is the copying process by which a cell duplicates its DNA

•Occurs during S phase of the cell cycle in the nucleus

• In order to do this, the enzyme DNA helicase moves along a molecule of DNA and breaks the weak hydrogen bonds between the nitrogen bases.

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DNA REPLICATION

When they do this they

“unzip” the ladder,

which comes apart

and the two sides of

the ladder separate.

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• DNA polymerase comes along

afterward and carries the individual

nucleotides to the site of replication

• builds the daughter strand by matching

new nucleotides to their complementary

bases on the parent strand

• DNA polymerase elongates the DNA

strand in the 5’-3’ direction only

• Because of this, DNA polymerase has to

work backwards on one strand

• DNA replication proceeds until each

chromosome is completely copied.

DNA REPLICATION

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DNA REPLICATION

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DNA REPLICATION

• Each new strand of DNA now has half

of the old strand that came apart

and half of a new strand that was just

created.

• At the end of replication, there are 2

new identical strands of DNA

• 1 side is from the original DNA

strand (parent/template)

• The other side is the newly formed

strand that was “copied”

(daughter)

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DNA REPLICATION

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DNA REPLICATION